First I'd compliment him on his outfit. Then I'd give them a snack. Then I'd try to find out his name. Then I'd find out where they met. Then I'd call the cops or his nurse, whichever was appropriate.

But my 3-yo would never be walking anywhere alone, so this would never come up. My oldest grandson is 10, they live 2 blocks from school through a dead-end cut-off, but across a busy street, and he is just this year allowed to walk home alone. His Mom doesn't play games with her kids' safety. Neither did HER mom (me).